A strength of a communication radio wave (hereinafter, sometimes referred to as an amount of electric field strength or a communication power) transmitted from each access point included in the wireless LAN can be included as an example of an index for evaluating a quality of the communication state of a wireless LAN such as an accessibility of a wireless LAN (that is, whether communication via the wireless LAN is possible or not, or to what extent excellent communication can be performed). For example, in Patent Literature 1, a technology is disclosed, in which a monitoring beacon is periodically transmitted to an access point, each wireless slave station (wireless terminal device) accommodated in the access point is caused to stop communication and to perform a measurement of the ambient electric field strength, triggered by receiving the monitoring beacon, and by notifying the access point of the measurement result, the presence or absence of interference in the vicinity of the access point due to a radio wave transmitted from another adjacent access point is investigated. In addition, a technology disclosed in Patent Literature 2 is a technology for measuring the electric field strength when the electric field strength in a mobile information terminal is equal to or lower than a threshold value.